The invention relates to a method for producing semiconductor laser components which each have a cooling element.
During the steady-state operation of a semiconductor component, in order to prevent the temperature of the semiconductor body of the component from rising, the amount of heat produced by power losses is continuously emitted to the environment. Semiconductors with very high power losses, such as laser diodes, require very efficient cooling apparatuses to ensure that the heat losses which occur are transported adequately from the semiconductor body to the environment. This heat transport is necessary in order to keep the temperature of the semiconductor body sufficiently low such that the semiconductor body is not damaged or degraded during operation. Power semiconductors such as laser diodes having a high output power are thus in some cases fit to a suitable heat sink even during production. This can be seen in the relative component datasheets (see, for example, the datasheet for the SPL CGxx laser diode, xx=81, 85, 94 or 98, Osram Opto Semiconductors, Jan. 1, 2000).
In one conventional production method for semiconductor laser components, the semiconductor bodies are separated and are then soldered onto a metallic heat sink, and contact is made with them. This method requires both the individual heat sinks and the individual semiconductor bodies to be supplied to the component placement apparatus and to be positioned with respect to one another. Furthermore, the components cannot be tested until the end of this production method, since, for many test procedures, the component must already have been cooled sufficiently at the time when the test is carried out. Otherwise, there is a risk of the component being damaged by the excessively large amount of heat developed when the test procedure is carried out.
It is accordingly an object of the invention to provide a method for producing semiconductor laser components which overcomes the above-mentioned disadvantageous of the prior art methods of this general type, and which in particular, allows the semiconductor bodies to be mounted at low cost and in a simple manner.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for producing semiconductor laser components, that includes a step of: providing a cooling element having an electrically insulating carrier that is formed as a plate having a main surface which is covered by a metal coating. The metal coating is then structured to form a number of chip mounting areas. In the next step, semiconductor laser chips are fit to these chip mounting areas, with one semiconductor laser chip being arranged on each chip mounting area. Finally, the semiconductor laser components are separated. This is done by subdividing the cooling element into a number of semiconductor laser components, with the semiconductor laser chips fit to them. The semiconductor laser components formed in this way each have at least one semiconductor laser chip and a part of the cooling element as a heat sink.
The structuring of the cooling element to form the chip mounting areas may include the formation of individual metal surfaces, including any surface treatments and solder coatings, and the formation of interconnects on the carrier. Furthermore, weak points may be formed in the carrier during this step.
In the case of the invention, the semiconductor laser chips are mounted on the cooling element before they are separated. This simplifies the mounting process, since the cooling element need be positioned only once for fitting a number of semiconductor bodies. Furthermore, the positioning of the semiconductor bodies is simplified, since, in contrast to cooling elements which have already been separated, the cooling element represents a very accurately defined mounting platform.
Since the number of positioning steps is reduced and it is easier to position the semiconductor bodies, the method can be carried out easily and at low cost.
In accordance with an added feature of the invention, the semiconductor bodies are tested in a further step before being separated, in which case the test time and the conversion time are advantageously kept short.
In accordance with an additional feature of the invention, optical elements for carrying the radiation produced or the radiation to be detected are mounted on the carrier, in a further step, before the separation process. These elements may be, for example, collimation optics for the generated laser radiation and elements for light injection into glass fibers, including the fiber retention mechanism. These elements must be aligned exactly with the semiconductor body. Since the mounting platform is defined accurately, and the positioning accuracy is hence also high, this can be done with high precision using the invention.
In accordance with another feature of the invention, the chip mounting areas are arranged in a matrix form. This is particularly advantageous when using automatic component placement machines, in order to keep the positioning times short.
In accordance with a further feature of the invention, the chip mounting areas are in the form of metal surfaces on the carrier. This allows the semiconductor bodies to be connected to the cooling element by soldered joints, which at the same time have very good electrical and thermal conductivity. Furthermore, since their thermal conductivity is high, the metal surfaces allow the heat to be distributed uniformly in the carrier located underneath, thus allowing heat to be transported efficiently.
In accordance with a further added feature of the invention, connecting pads are formed on the metal surfaces which form the chip mounting areas, and the semiconductor bodies are fit and mounted on them (chip connecting pads). These connecting pads are advantageously covered with an electrically and thermally conductive adhesion means such as a solder. This allows the invention to be used in automatic component placement machines, with reliable soldered joints being produced automatically in the process.
In accordance with a further additional feature of the invention, interconnect structures are formed on the carrier of the cooling element. In this case, subareas of the interconnect structures are used as connecting pads for wire connections which make electrical contact with the semiconductor bodies (wire connecting pads). It is a major advantage that the interconnects can be used to actuate the semiconductor bodies electrically, so that their functionality can be tested before they are separated. In contrast, components according to the prior art cannot be tested until after they have been separated, since the heat sink is not fit until after the separation process and the component must be cooled adequately for many test procedures.
The advantage of testing before separation is that the test apparatus need be connected to the interconnect system only once for a number of components and thus the test times are reduced. One particular advantage is that a number of components can be tested simultaneously. Depending on the configuration of the interconnects on the cooling element, it is in this case possible to carry out individual tests, group tests or a simultaneous test of all the semiconductor bodies that have been installed. These test options are particularly advantageous because of their flexibility and the time that is saved when they are carried out simultaneously. The term test procedure in this case refers to functional tests, aging and life tests and, in particular, to forming cycles, which are also referred to as xe2x80x9cburn-inxe2x80x9d, some of which are carried out at full load and are thus generally feasible only when sufficient cooling is provided.
In accordance with yet an added feature of the invention, metallic surfaces are likewise formed on the second main surface of the carrier, and are associated with the chip mounting areas on the first main surface. The layered structure of metal-carrier-metal formed in this way is distinguished by efficient heat transport, with low and homogeneous thermal expansion at the same time. If the metals and the carrier material together with the respective layer thicknesses are chosen appropriately, the coefficient of expansion of the cooling element can be matched precisely to the thermal coefficient of expansion of the semiconductor body. This matching is a highly advantageous way of avoiding thermal alternating loads leading to stresses in the soldered joints between the semiconductor body and the cooling element, which can lead to the soldered joints fracturing.
A ceramic material with high thermal conductivity, such as AlN or BN, is preferably used as the carrier material. An AlN carrier can advantageously be connected to a copper coating. Such direct bond copper materials (DBC) are distinguished by high thermal conductivity, while at the same time have low thermal expansion. It is particularly advantageous in this case that, if designed appropriately, the assembly has a thermal coefficient of expansion which is virtually the same as the thermal coefficient of expansion of GaAs. When using a DBC material, the invention is thus particularly suitable for use as a cooling element for GaAs semiconductor bodies, such as laser diodes based on GaAs and having a high output power.
In accordance with yet an additional feature of the invention, weak points are formed between the areas for accommodating the semiconductor bodies. After being mounted and, if appropriate, after carrying out the test procedures, the cooling element can thus easily be subdivided by fracturing it.
In accordance with yet another feature of the invention, the carrier has a number of layers, and the coating which is adjacent to the first main surface is electrically insulating. A multilayer carrier can be matched very well to the semiconductor body and to the intended field of use of the component, in terms of the expansion behavior, the mechanical strength and the thermal conductivity.
In accordance with a concomitant feature of the invention, the metal coating on the carrier, the chip mounting areas and, if appropriate, the associated surfaces on the opposite main surface are in the form of a number of layers. Surface treatment of the metallic surfaces, in the form of a thin noble-metal coating, is particularly advantageous in this case. Such surface treatment improves the solderability of the metal surfaces, while at the same time providing corrosion protection.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for producing semiconductor laser components, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.